Flow Rate Accuracy of a Fluidic Delivery System

ABSTRACT

Improving the accuracy of the flow rate of a valve in a fiuidic delivery device in which a desired flow rate may be achieved by varying the duty cycle of the valve. The flow rate of fluid delivery from the valve over its lifetime is stabilized by minimizing the voltage OPENING time of the valve to account for valve and piezoelectric actuator drift. Also, the valve OPENING time of one or more fiuidic parameters that impact on the flow rate delivery by the valve and differ among fiuidic delivery devices is compensated to optimize the flow rate accuracy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/255,666, filed Oct. 22, 2008, which is acontinuation-in-part of U.S. patent application Ser. No. 11/259,413,filed Oct. 26, 2005, each of which is herein incorporated by referencein their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a system and method for improvingthe flow rate accuracy of a fluidic delivery system.

2. Description of Related Art

Fluidic delivery devices have widespread use in the medical field withthe use of implantable drug infusion delivery devices for delivering adrug or other fluid to the body at specified flow rates over time. Theimplantable drug infusion delivery device is generally programmed via acontrol unit disposed external to the body and in communication with theimplantable drug infusion delivery device via a communication interface,preferably a wireless communication interface such as RF telemetry.There are many types of drug infusion delivery devices or pumps such asperistaltic, bellows, piston pumps. U.S. Patent Application PublicationNo. 2007/0090321 A1 discloses one exemplary piston pump, which is hereinincorporated by reference in its entirety.

With the advent of such technology, it is possible to program a specificdrug profile over time to be dispensed or delivered from the implantabledrug infusion delivery device. Such functionality may be used fordispensing a wide range of drugs such as pain medication or the deliveryof insulin as well as many others. Despite the advantages associatedwith using an implantable drug infusion delivery device to automaticallydispense a drug over time based on a programmed drug delivery profile,its efficacy depends on the ability of the implantable drug infusiondelivery device to dispense the medication at a substantially constantflow rate on which the programmed drug delivery profile was based.Otherwise, if the flow rate, of fluid dispensed by the drug infusiondelivery device varies over time then the programmed drug deliveryprofile will result in either an underdosage or an overdosage. Anydeviation in the drug dispensed may have unintended if not harmful, andin some cases life threatening, health effects for the patient.

It is therefore desirable to develop an improved system and method forstabilizing the flow rate of a fluidic delivery device over its lifetimeand also to optimize the flow rate accuracy of a fluid delivered from afluidic delivery device to compensate for one or more fluidic parametersthat compromise the flow rate.

SUMMARY OF THE INVENTION

The present invention is directed to a system and method for improvingthe accuracy of the flow rate of a valve in a fluidic delivery device inwhich a desired flow rate may be achieved by varying the duty cycle ofthe valve. The flow rate of fluid delivery from the valve over itslifetime is stabilized by minimizing the voltage OPENING time of thevalve to account for valve and piezoelectric actuator drift. Also, thevalve OPENING time of one or more fluidic parameters that impact on theflow rate delivery by the valve and differ among fluidic deliverydevices is compensated to optimize the flow rate accuracy.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other features of the present invention will be morereadily apparent from the following detailed description and drawings ofillustrative embodiments of the invention wherein like reference numbersrefer to similar elements throughout the several views and in which:

FIG. 1 a is a perspective view of a valve assembly 10 for a fluidicsystem;

FIG. 1 b is a cross-sectional view of the valve assembly of FIG. 1 a;

FIGS. 2 a-2 c show different exemplary flow rates for a valve assemblyhaving a block of 400 seconds by varying the duty cycle in accordancewith the present invention;

FIG. 3 a is an exemplary graphical representation of the actual valveOPENED and valve CLOSED timing of the valve assembly in FIG. 1 b overtime;

FIG. 3 b is an exemplary graphical representation of the dischargesignal for discharging of the piezoelectric actuator;

FIG. 3 c is an exemplary graphical representation of the piezoelectricactuator voltage;

FIG. 3 d is an exemplary graphical representation of the PWM chargeinput signal to the charge pump circuitry in FIG. 4 wherein the PWMcharge input signal has been divided into 20 PWM units each having itsassociated PWM parameters;

FIG. 3 e is an enlarged exemplary graphical representation of thepiezoelectric actuator voltage from FIG. 3 b during a single PWM chargeinput signal comprising 20 PWM units;

FIG. 3 f is an enlarged exemplary graphical representation of a singlePWM charge input signal comprising 20 PWM units;

FIGS. 3 g-3 j represent waveforms depicting valve state, dischargesignal and actuator voltage signal associated with an exemplary firstvalve OPENING time;

FIGS. 3 k-3 n represent waveforms depicting valve state, dischargesignal and actuator voltage signal associated with an exemplary secondvalve OPENING time greater than the first valve OPENING time depicted inFIGS. 3 g-3 j;

FIG. 4 is an exemplary schematic circuit diagram for generating a PWMcharge input signal to achieve a predetermined threshold voltage of 60Vacross the piezoelectric actuator in FIG. 2 and open the valve;

FIG. 5 shows an exemplary single PWM charge input signal generated for asingle block of 400 seconds duration at a constant power supply voltage,wherein the PWM charge input signal is subdivided into 20 PWM units andvarying the OFF time of the transistor in FIG. 4 while the transistor ONtime remains constant;

FIG. 6 shows exemplary PWM units over a period of time (e.g., severalyears) for depicting a decreasing power supply voltage, wherein the ONtime of the transistor in FIG. 4 is varied while the transistor OFF timeremains constant;

FIG. 7 is a graphical representation of the weight of fluid delivered bya fiuidic delivery device over time without taking into considerationthe compliance effect of the seal;

FIG. 8 is a graphical representation of the weight of fluid delivered bya fiuidic delivery device over time showing the compliance effectproduced by the seal;

FIGS. 9 a-9 g show as an illustrative example of the compliance effecton an air bubble trapped in a valve as it opens and closes;

FIG. 10 is an exemplary flow chart depicting the process in determiningthe Total Compensated Valve OPENING Time Per Block to compensate for oneor more of the calibrated fiuidic parameters; and

FIG. 11 is an exemplary schematic diagram of an external control deviceused to program an implantable drug delivery device and the specificmemory architecture within the implantable drug delivery device.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a and 1 b depict a valve assembly 10 for use in a fiuidicsystem, e.g., implantable drug infusion delivery system. Valve assembly10 has a body 12 which defines a bore 14 that is sized and shaped toslidably receive a piston 16, as shown in the cross-sectional view ofFIG. 1 b. Body 12 further includes an inlet passage 18 that providesfluid communication between a fluid reservoir 62 and a lower end 20 ofbore 14. In addition, body 12 includes an outlet passage 22 fortransporting fluid from the valve assembly 10 (when the valve is in anOPEN state) to a conduit that delivers the fluid to a desired site ofinterest.

In this exemplary valve structure or assembly 10, piston 16 ispositioned within bore 14 and includes an upper sealing end 24 thatsupports a disc-shaped seal 26. Piston 16 has an opposite lower end 28,which includes a downwardly-directed boss 30 sized and shaped to receiveone end of a compression spring 32. In addition, piston 16 has definedtherein a circumferentially disposed spiral groove 34 (positioned alongthe sidewall and extending substantially the length of the piston 16)providing fluid communication between the lower end 20 of bore 14 (andinlet passage 18) and upper sealing end 24 of piston 16. Fluid enteringthe lower end 20 of bore 14 (under pressure from the reservoir 62)freely advances between the piston 16 and the bore 14 via spiral groove34.

As shown in FIG. 1 b, spring 32 is positioned between lower end 28 ofpiston 16 and the lower end 20 of bore 14. Spring 32 biases piston 16and disc-shaped seal 26 upwardly towards an upper end 36 of bore 14.

Securely attached (i.e., preferably hermetically sealed) to body 12 andpositioned over upper end 36 of bore 14 is a contact disc 38 that ispreferably made from a rigid material such as a metal. Contact disc 38has a central opening 40 defined therein and an integrally formed,downwardly-directed contact ridge 42. Contact ridge 42 is formedpreferably concentrically to central opening 40 and sized and shaped tofit within bore 14, as shown in FIG. 1 b. Contact disc 38 is positionedso that contact ridge 42 aligns with disc-shaped seal 26. As piston 16is pushed upwardly by spring 32, disc-shaped seal 26 is pressed into asealing contact with circular contact ridge 42 thereby closing the valveassembly 10, as described in greater detail below.

Projecting from upper sealing end 24 of piston 16 is a substantiallyaxially-aligned contact pin 25. Contact pin 25 is adapted to bedisplaceable within substantially central opening 40 defined in contactdisc 38 while an upper contact surface 27 extends and remains abovecontact disc 38. Downward displacement of contact pin 25 causes piston16 to separate disc-shaped seal 26 from sealing, contact of contactridge 42 of contact disc 38 thereby opening the valve assembly.

Securely affixed to body 12 (i.e., preferably hermetically sealed) andpositioned over upper end 36 of bore 14 and contact disc 38 is a portalsupport ring 44 which includes a central opening 46 and defines a lowersurface 48. Attached to the lower surface 48 and covering the centralopening 46 is a thin, flat coin-like, flexible membrane 50 positionedabove an upper surface 52 of contact disc 38 a predetermined distance sothat a collection space 54 is defined therebetween.

Membrane 50 is generally made from a relatively strong resilient metalsuch as titanium and is brazed or welded to the lower surface 48 ofportal support ring 44. Similarly, portal support ring 44 is brazed tobody 12 so that piston 16, disc-shaped seal 26, spring 32, inlet passage18, outlet passage 22, and contact disc 38 all define a “wet side”relative to membrane 50 (lower side) and are all hermetically sealedwithin the valve body 12 yet isolated from everything located above andoutside the valve body 12 by a space which defines a “dry side” relativeto membrane 50. Upper surface 27 of contact pin 25 abuts against a lowersurface 51 of membrane 50. Spring 32 biases contact pin 25 into firmcontact with lower surface 51 of membrane 50.

The valve assembly 10 is opened and closed repeatedly at a predeterminedfrequency by applying the mechanical displacement generated by apiezoelectric actuator or piezo crystal 53 (in response to an appliedelectrical signal) to move piston 16 axially up and down. An actuationpin 55 is used to connect the piezoelectric actuator 53 to contact pin25 indirectly through membrane 50, as described below. Actuation pin 55is substantially axially aligned with contact pin 25.

In operation of the above described valve assembly 10, fluid (e.g., adrug in liquid form) is supplied to inlet passage 18 under pressure froma reservoir 62, but regulated by a fiuidic pressure regulator or fiuidicrestrictor 60 such as a fiuidic chip. Fluid enters lower end 20 of bore14. When piston 16 is forced downwardly within bore 14 against theaction of spring 32 fluid from the reservoir 62 passes through thefluidic pressure regulator 60 and into the inlet passage 18 moving pastpiston 16 by way of groove 34 to the top of piston 16. Downwarddisplacement of piston 16, in turn, causes disc-shaped seal 26 toseparate from contact ridge 42 thereby allowing fluid (still underregulated pressure) to pass through central opening 40 defined incontact disc 38 and enter the collection space 54. Any fluid withincollection space 54 will be forced into outlet passage 22 and eventuallydirected to a desired site of interest (such as a desired treatment areaof a patient's body).

Downward movement of piston 16 is controlled by applying a specificelectrical signal to the piezoelectric actuator 53 that as a resultthereof deforms with a slight downward displacement. This slightdownward movement is transferred to the contact pin 25 through theactuation pin 55 and flexible membrane 50. Therefore, the particularelectric signal applied to the piezoelectric actuator 53 will indirectlycontrol the opening of the valve assembly 10 and therefore the amountand flow rate of fluid passing from inlet passage 18 to the outletpassage 22.

The flow rate of the fluid being dispensed from the outlet passage 22 isadjustable by varying the ratio of the valve OPENED time/valve CLOSEDtime (ratio of the duration of time in which the valve is in respectiveOPENED and CLOSED states) of the valve assembly 100 by means of thepiezoelectric actuator 53. Pressurized reservoir 62 is fluidly connectedto the fluidic regulator or restrictor 60. The outlet of the flowregulator or restrictor 60 is, in turn, fluidly connected via an inletpassage 18 to the bore 14 in which piston 16 is displaceable therebyopening and closing the valve. While in an OPENED state fluid ispermitted to pass through the valve assembly 10 and dispensed via theoutlet passage 22. When the valve assembly 10 is in an OPENED state, thefluidic restrictor 60 and the differential pressure across it define aconstant flow rate at the outlet passage 22 of the fluidic deliverysystem.

The constant flow rate dispensed from the valve assembly can beadjusted, as desired, by varying the ratio of the valve OPENED time tothe valve CLOSED time hereinafter referred to as the duty cycle. Duringa predetermined period of time or duration (hereinafter referred to as a“block”) the valve assembly opens once (the piezoelectric actuator ischarged) and the valve closes once (the piezoelectric actuator isdischarged). Knowing the predetermined block duration (e.g., 400seconds), the flow rate for the valve assembly can be determined basedon the duration of the valve OPENED time versus the valve CLOSED time.

FIGS. 2 a-2 c depict different flow rates, e.g., 4 ml/day, 2 ml/day and1 ml/day, respectively. A maximum constant flow rate of 4 ml/day isrepresented in the first example shown in FIG. 2 a in which for each 400second block the valve OPENED time is the virtually the full 400seconds, while the valve CLOSED time is extremely short, almost zero (asdenoted by the enlarged view of the first 400 second block). The secondexample, shown in FIG. 2 b shows for each 400 second block the valveOPENED time and the valve CLOSED time are equally 200 seconds durationeach. This would result in a flow rate half that of the maximum flowrate (e.g., 4 ml/day shown in FIG. 2 a) for a constant flow rate of 2mL/day. A third example is depicted in FIG. 2 c in which the valveOPENED time is for 100 seconds while the valve CLOSED time is 300seconds. The third duty cycle example will produce a constant flow rateof 1 mL/day. By varying the duty cycle (i.e., the ratio of the valveOPENED time to the valve CLOSED time) a desired constant flow rate offluid dispensed from the valve may be realized.

FIG. 3 a is an exemplary graphical representation of the opening andclosing over one hour of valve assembly 10 in FIGS. 1 a and 1 b. Thereare a total of 9 blocks within one hour depicted in FIG. 3 a, each blockbeing 400 seconds. The smallest time interval over which the valve canbe programmed by a user is 1 hour increments. Each 400 second blockcomprises a valve OPENED time and a valve CLOSED time of equal duration(e.g., 200 seconds). By way of example, the maximum flow rate defined bythe flow restrictor 110 and the differential pressure across it is 2ml/day. This example is merely for illustration purposes and any one ormore of the parameters, may be selected as desired, including: (i) theduration or time period of the block (e.g., 400 seconds), (ii) minimumprogramming period of time (for example, one hour), (iii) maximum flowrate in a 24 hour period, (iv) valve OPENED time, and (v) valve CLOSEDtime.

Valve assembly 10 is a mechanical device that forms a fluid channelcapable of being either opened or closed by a piezoelectric actuator 53.When actuated the piezoelectric actuator 53 bends and moves the plungeror piston 16 downward via actuation pin 55. As a result, the valveopens. A predetermined threshold voltage of 60 V (as denoted by line 301in FIG. 3 c) is needed to be applied across the piezoelectric actuatorin order to open the valve assembly 10. The voltage across thepiezoelectric actuator 53 is supplied by power supply (e.g., a battery)and associated charge pump circuitry an example of which is shown inFIG. 4.

Circuitry 600, in FIG. 4, is used to charge the piezoelectric actuator53 to the predetermined threshold voltage of 60V that, in turn, opensthe valve assembly 10 (in FIG. 1 b). Power supply 605, for example, abattery is used to power circuitry 600. The battery may be arechargeable battery or a non-rechargeable battery. As represented bythe shaded PWM charge input signal 307 in FIG. 3 d, the piezoelectricactuator 53 is charged once every block (e.g., 400 seconds) regardlessof the flow rate, therefore the lifetime of the power supply isindependent of the flow rate. A capacitor 610 is connected in parallelwith power supply 605. Transistor 620, for example a Field EffectTransistor (FET) is periodically switched ON and OFF in response toreceiving a Pulse Width Modulated (PWM) charge pump input or drivingsignal generated by processor 640 to allow energy received from thepower supply 605 and stored in an inductor 615 to charge thepiezoelectric actuator 53.

Voltage Scaling Circuitry 625 scales down the relatively high measuredvoltage or charge stored by the piezoelectric actuator 53, preferably bya factor of 40, and generates a Measured Piezoelectric Voltage FeedbackSignal that is received as input to the processor 640. A comparison ismade by an analog comparator comprising processor 640 between the scaleddown Measured Piezoelectric Voltage Feedback Signal and a similarlyscaled down predetermined stored reference voltage of 1.2V (representingthe predetermined threshold voltage of 60V scaled down by the samefactor of 40 as that of the Measured Piezoelectric Voltage FeedbackSignal) for actuating the piezoelectric actuator 53. If the scaled downMeasured Piezoelectric Voltage Feedback Signal is less than 1.2V thenthe PWM charge pump input signal is generated causing the transistor 620which receives it to switch ON and OFF and allow the stored charge ininductor 615 to be applied to the piezoelectric actuator 53. TheMeasured Piezoelectric Voltage Feedback signal is continuously monitoreduntil it reaches 1.2V at which point processor 640 triggers an interruptthat cuts off the PWM charge pump input signal causing transistor 620 toswitch OFF permanently thereby opening the circuit and preventing theflow of energy from the power supply 605 to the inductor 615.Accordingly, energy from the power supply 605 is only consumed duringcharging of the piezoelectric actuator 53 until reaching thepredetermined threshold voltage of 60V. Once the valve is open (i.e.,the piezoelectric actuator is charged to the predetermined thresholdvoltage of 60V) it is maintained opened (i.e., the piezoelectricactuator substantially retains its charge with relative small leakageover time (represented by the drop in voltage over the time representedby reference element 308 in FIG. 3 d) due to relatively low leakagediodes D1 arid D2) without requiring energy. At the end of the valveOPENED time (represented by each “OPENED” block in FIG. 3 a), processor640 generates a Disable Signal or Discharge Signal (shown in FIG. 3 b)that is received as input by Voltage Discharge Circuitry 630 todischarge the charge built up across the piezoelectric actuator 53 fromthe predetermined threshold voltage of 60V (represented by referenceelement number 301) down to the valve OPENING voltage 302 that differsamong fiuidic delivery devices. Thus, the only negligible energyexpended to discharge the piezoelectric actuator 53 and close the valveis the power required by the processor to generate the discharge pumpsignal and the energy dissipated by the transistor when switching itsstate.

The input of the charge pump circuitry is a PWM signal, such as theexemplary PWM signal shown in FIG. 3 d. The output of the charge pumpcircuitry is the voltage applied across the piezoelectric actuator 53 asshown in FIG. 3 c. It will take a predetermined period of timerepresented by reference element 307, referred to as rise time, for thevoltage applied across the piezoelectric actuator 53 to attain thepredetermined threshold voltage of 60V necessary to open the valve 115.

Over the lifetime of the valve assembly the valve OPENING voltage(reference element 302 in FIG. 3 c) for a particular valve will increasedue to drift of the piezoelectric actuator behavior. For instance,initially at the time of implantation, a valve may have a valve OPENINGvoltage of 55V and after the passage of a period of time, for example,several years, the valve OPENING voltage may rise to 57V. Variation inthe valve OPENING voltage over the lifetime of the valve assembly willresult in undesirable deviation in the accuracy of the programmed flowrate of the fluid being dispensed from the valve.

Despite the variation in valve OPENING voltage, the accuracy of the flowrate of fluid delivered from the fluidic delivery device may bestabilized or maintained over its lifetime by minimizing the valveOPENING time (i.e., the time it takes to the charge applied across thepiezoelectric actuator to go from 0V to the opening voltage 302) toinsure that the valve opens quickly. FIGS. 3 g-3 n illustrate thisconcept by depicting two different valve OPENING times. A firstexemplary valve OPENING time is shown in FIGS. 3 g-3 j, while a secondexemplary valve OPENING time is shown in FIGS. 3 k-3 n. The valveOPENING time in FIGS. 3 k-3 h is greater than that shown in FIGS. 3 g-3j. As a result, the slope of the waveform in FIGS. 3 k-3 n is smaller(i.e., less steep) than that shown in FIGS. 3 g-3 j. Over time the valveOPENING voltage (reference element 302 in FIGS. 3 j and 3 n) willincrease due to drift of the valve and piezoelectric actuator asrepresented by reference element 302′. At the valve OPENING voltage302′, the valve OPENED time in FIGS. 3 g, 3 k is reduced to that shownin FIGS. 3 h, 3 l, respectively, thereby compromising the accuracy ofthe flow rate delivered by the valve. Initially, the deviation or errordue to reduced valve OPENED time resulting from this increase in valveOPENING voltage may be negligible, but over the lifetime of the valveOPENING voltage will continue to rise and eventually may result in asignificant underdosage in the amount of fluid delivered. The relativelylarge valve OPENING time of the example in FIGS. 3 k-3 n reduces thevalve OPENED time from that shown in FIG. 3 k to that shown in FIG. 3 lby an amount identified as “Error on one Valve OPENED time” (FIG. 3 k).It has been recognized that reducing or minimizing the valve OPENINGtime (as represented by the graphical waveform in FIGS. 3 g-3 j incomparison to that shown in FIGS. 3 k-3 n) minimizes any reduction invalve OPENED time, as identified by the smaller “Error on one ValveOPENED time” shown in FIG. 3 g compared to that in FIG. 3 k. It istherefore desirable to minimize the valve OPENING time in order tominimize the reduction in valve OPENED time resulting from an increasein valve OPENING voltage over the lifetime of the valve to stabilize theflow rate.

The valve OPENING time can be minimized by dividing the PWM charge inputsignal for driving the charge pump into multiple PWM units, with eachPWM unit applying for that duration of time its own associated orcorresponding set of PWM parameters (e.g., frequency, duty cycle, andduration for which the PWM charge input signal should be generated(transistor OH time/transistor OFF time)). It is contemplated and withinthe scope of the present invention for each of the multiple PWM units tobe equal or non-equal, as desired. There is an optimum number of PWMunits that may be determined for the particular piezoelectric actuatorfor minimizing the valve OPENING time. On the one hand, if the number ofPWM units is less than the optimum number of PWM units then the minimumvalve OPENING time will not be realized. On the other hand, if theoptimum number of PWM units is exceeded, no further reduction in valveOPENING time will be realized.

An exploded view of a single PWM charge input signal (reference element307 from FIG. 3 d) is shown in FIG. 3 f. In the example shown in FIG. 3f, the PWM charge input signal is divided into 20 PWM units each havingis own associated PWM parameters. The 20 PWM units together for a singleblock are referred to as a PWM group (PWM charge input signal). At thebeginning of each block (e.g., 400 second duration block) the PWM chargeinput signal is generated to drive the charge pump. The graphicalrepresentation shown in FIG. 3 d shows the PWM charge input signaldriving the charge pump until the voltage applied across thepiezoelectric actuator 53 reaches the 60V predetermined thresholdvoltage (reference element 301 in FIG. 3 c) necessary to displace thepiezoelectric actuator and thus open the valve 115. When the voltageapplied across the piezoelectric actuator 53 reaches the 60Vpredetermined threshold voltage the PWM charge input signal is cut offor ended by the processor 640 (FIG. 4). At the end of the valve OPENEDtime in FIG. 3 a, a discharge signal is generated (FIG. 3 b) by theprocessor 640 and received by the Voltage Discharge Circuitry 630causing the voltage stored across the piezoelectric actuator 53 to dropfrom 60V to the valve OPENING voltage (reference element number 302 inFIG. 3 c).

In still another improvement of the present invention, to furtheroptimize valve OPENING time the transistor ON time and/or OFF time foreach PWM unit of a PWM charge input signal may be adjusted asrepresented by the examples shown in FIGS. 5 and 6. For a constantbattery voltage, the time duration for each block (e.g., 400 seconds) isfixed and the transistor ON time (period of time for which thetransistor 620 is ON) is also fixed, however, the transistor OFF time(period of time for which transistor 620 is OFF) may vary among thedifferent PWM units in a particular PWM group (i.e., a particular PWMcharge input signal). Since the maximum current drawn from the powersupply 605 is limited, the transistor ON time is fixed to limit thecurrent drawn. The charge pump draws current from the power supply 605when the PWM charge input signal is generated. The transistor OFF timeduration must be sufficient to insure complete transfer of charges fromthe inductor 615 that stores the charge to the piezoelectric actuator53. Since the time to transfer charge from the inductor 615 to thepiezoelectric actuator 53 depends on the charge already stored in thepiezoelectric actuator 53 at any given time, the transistor OFF timevaries among PWM units within a particular PWM group.

In addition, over time, for example, the passing of several years, thepower supply voltage will decrease and thus the amount of charge builtacross the inductor 615 will also decrease. It is therefore advantageousto vary the transistor ON time when the power supply voltage changes inorder to optimize the valve OPENING time. Similarly, the transistor OFFtime may be adjusted in order to allow sufficient time for chargetransfer from the inductor 615 to the piezoelectric actuator 53, asdescribed in the preceding paragraph.

FIG. 5 shows an exemplary PWM charge input signal (PWM group) generatedfor a single block of 400 seconds duration at a constant power supplyvoltage. The exemplary PWM charge input signal (PWM group) shown isdivided into 20 PWM units of equal duration (PWM unit-1, . . . unit-N, .. . unit-20). The first PWM unit (PWM unit-1) is generated at thebeginning of the 400 second block when the charge across thepiezoelectric actuator 53 is 0V. With each subsequent PWM unit thevoltage across the piezoelectric actuator increases until thepredetermined threshold voltage (e.g., 60V) is applied to thepiezoelectric actuator with the last PWM unit (PWM unit-20). All PWMunits have a constant or fixed transistor ON time duration in which thePWM charge input signal is generated. The transistor ON time duration islimited by the current drawn from the power supply (e.g., battery) andtherefore remains constant or fixed among all PWM charge input signals(PWM groups) and all PWM units within a particular PWM charge inputsignal (PWM group). Each PWM unit has a fixed transistor OFF timeduration in which the PWM charge input signal is not generated, however,the transition OFF time duration may vary among PWM units in aparticular PWM group. As seen in FIG. 5, the transistor ON time for allPWM units is constant or fixed. The transistor OFF time duration isconstant in any particular PWM unit such as within PWM unit-1, unit-N orunit-20. However, the transistor OFF time duration varies among PWMunit-1, unit-N and unit-20. It is clearly shown in FIG. 4 that thetransistor OFF time duration is reduced from PWM unit-1 to PWM unit-20.This adjustment in the transistor OFF time duration of the PWM signal inany particular PWM unit takes into account the fact that the chargestored in the piezoelectric actuator is built up over time. Aspreviously mentioned, the time necessary to transfer charge from theinductor 615 to the piezoelectric actuator 53 decreases as the chargestored in the piezoelectric actuator 53 increase. Accordingly, thetransistor OFF time duration representing the time needed to transferthe charge from the inductor 615 to the piezoelectric actuator 53 may bereduced.

FIG. 6 shows exemplary PWM units over a period of time (e.g., severalyears) for depicting a decreasing power supply voltage. Note that incontrast to that shown in FIG. 5, the PWM units illustrated in FIG. 6 donot represent PWM units within a single PWM group. Instead, what isrepresented is three PWM units at different instances of time overseveral years. Since the power supply voltage decreases over relativelylong periods of time (e.g., several years) the different PWM units shownillustrate merely snap shots in time in which the battery voltagedecreases relative to that of an earlier in time PWM unit. In thisexample during the time intervals between the PWM units depicted thebattery voltage remains constant or fixed. Referring to FIG. 6, the PWMunits will be addressed from top to bottom. The battery voltagemeasurement at the time of the top PWM unit was 3.4V. At some point intime thereafter, the measured battery voltage dropped to 2.8Vcorresponding to the intermediate PWM unit. After the duration of someperiod of time thereafter, a battery voltage of 2.4V was measured at thetime of the bottom PWM unit. The transistor OFF time remains constant orfixed among all PWM groups and all PWM units within a particular PWMgroup. However, the transistor ON time is adjusted to account fordecreasing power supply voltage over time. Specifically, the transistorON time duration increases as the power supply voltage decreases. Thereasoning for this is because since the power supply voltage decreasesover time then the transistor ON time must increase in order to allowthe same amount of energy relative to when the power source was fullycharged to flow from the power supply 605 to the inductor 615 andsubsequently to the piezoelectric actuator 53. In summary, a longertransistor ON time is required when the power supply 605 is not fullycharged in order to transfer the same amount of energy from the powersupply 605 to the inductor 615 and subsequently to the piezoelectricactuator 53 then would be transferred from a power supply 605 having agreater voltage and by using the same transistor ON time.

The two concepts presented separately in FIGS. 5 and 6 may be combinedwherein when the power supply voltage remains constant or fixed thetransistor OFF time for a particular PWM unit is adjusted, while thetransistor ON time for a particular PWM unit is adjusted when the powersupply voltage decreases.

Thus far, the accuracy of the flow rate has been maintained orstabilized for a particular fiuidic delivery device in which the flowrate may vary over time due to such factors as: (i) mechanical driftover time, (ii) deformation of the seal with usage over time, and (iii)depletion of energy provided by the power supply. Accordingly, thepreviously described adjustments to the valve OPENING time maintains orstabilizes the flow rate accuracy for any given fiuidic delivery device.

It is also recognized that the flow rate accuracy may be affected byparameters that differ from one fiuidic delivery device to another. Theflow rate accuracy may be dependent on any number of one or more factors(hereinafter collective referred to as “fiuidic parameters”) such as:(i) the compliance effect, (ii) the maximum flow rate for the givenfiuidic delivery device, (iii) the pressure on the fluid in thereservoir which is dependent on the temperature (temperature-pressurerelationship of reservoir fluid), (iv) valve OPENING time (time for thecharge applied across the piezoelectric actuator to go from 0V to thevalve OPENING voltage, e.g., reference element 302 in FIG. 3 c), and (v)valve CLOSING time (time required to discharge the charge stored acrossthe piezoelectric actuator from the 60V predetermined threshold voltage(reference element 301 in FIG. 3 c) to the valve OPENING voltage(reference element 302 in FIG. 3 c)). Accordingly, it is desirable tooptimize the accuracy of the flow rate of fluid delivery by compensatingfor differences among fiuidic delivery devices with respect to any oneor more of these fiuidic parameters. Each of these fiuidic parameterswill be addressed separately.

Referring once again to FIG. 1 b, the contact disc 38 in the valveassembly 10 is positioned so that contact ridge 42 aligns with thedisc-shaped seal 26. As piston 16 is pushed upwardly by compressionspring 32, disc-shaped seal 26 is pressed into a sealing contact withcircular contact ridge 42 thereby closing the valve assembly. When thevalve is closed, the elevated or higher pressure from the reservoir 62compresses the seal 26 downward toward the lower end 20 of bore 14. Ifthe seal 26 was not made of a compressible material, the volume of fluiddelivered by the fiuidic delivery system would correspond to thegraphical representation shown in FIG. 7. It is represented by thegraphical waveform in FIG. 7 that when the valve is in an OPEN state aconstant flow rate (denoted by a graphical waveform haying asubstantially constant slope) of fluid is delivered. On the other hand,while the valve is in a CLOSED state; a fixed or unchanging flow rate isexperienced (as denoted by the substantially horizontal waveform). Thewaveform in FIG. 7 transitions directly from a substantially horizontalwaveform to a constant flow rate as represented by that portion of thewaveform having a constant positive slope.

However, seal 26 is made of a compressible material and hence FIG. 7fails to take into consideration the fluid dispensed from the valve whentransitioning from the CLOSED state to the OPENED state due to what isreferred to as the compliance effect of the seal. Every time the valveassembly transit ions from a CLOSED state to an OPENED state there is atransition period before realizing a constant flow rate. This transitionperiod is denoted by the substantially vertical line (segment “3”) shownin FIG. 8 and hereinafter referred to as a “compliance effect.” This“compliance effect” occurs because the seal 26 is made from acompressible material, e.g., silicon.

The compliance effect due to the compressible seal 26 can be explainedby analogy to an air bubble lodged in a valve. FIGS. 9 a-9 g depict thisair bubble example. In FIG. 9 a, the valve is open and the air bubble isat its lowest pressure. A constant flow rate will be dispensed from thevalve as illustrated by that portion of the graphical waveform having asubstantially constant slope (segment “1”). FIG. 9 b shows the valveimmediately after transitioning from an OPENED state to a CLOSED state.Once the valve is closed a fixed or unchanging flow rate is experienced(as denoted by the substantially horizontal waveform, e.g., segment“2”), as shown in FIG. 9 c. While the valve is in this CLOSED state,pressurized fluid from the reservoir compresses against thereby reducingin size the air bubble (FIG. 9 c). Accordingly, the pressure, in the airbubble is greater when the valve is in a CLOSED state than when thevalve is in an OPENED state. Lastly, FIG. 9 d depicts the reopening ofthe valve. Since the bubble was in a compressed state when the valve wasclosed, upon opening the valve the bubble must first return to itsdecompressed or equilibrium state. This decompression is represented bythe vertical portion of the waveform (segment “3”) in FIG. 9 d. Althoughdepicted as a vertical segment, in actuality such decompression orequilibrium occurs extremely quickly over a relatively short period oftime. During decompression undesirably some unaccounted for fluid willbe dispensed from the outlet passage 22 of the fluidic delivery devicethereby compromising the accuracy of the flow rate. Once the pressurehas been equalized, then the fluid will once again be dispensed from theoutlet passage 22 at a substantially constant flow rate, as representedby the graphical portion of the waveform having a constant slope(segment “4”) in FIG. 9 e. This compliance effect is produced each timethe valve transitions from a CLOSED state to an OPEN state. Lastly, FIG.9 f depicts the transitioning of the valve from the OPENED state to theCLOSED state, whereby the air bubble is once more compressed in size dueto the pressurized fluid from the reservoir. A fixed or unchanging flowrate is experienced (as denoted by the substantially horizontalwaveform, e.g., segment “5”), as shown in FIG. 9 g, while the valve isin the CLOSED state.

There is no air bubble in a valve assembly. Instead, the air bubbleexample shown in FIGS. 9 a-9 g is merely an illustrative tool forunderstanding what in actuality occurs in the valve assembly 10 shown inFIG. 1 b wherein the compressible seal 26 produces a similar complianceeffect. Every valve in which a compressible material is in contact witha rigid material will result in an analogous compliance effect. Thecompressible material, that is, seal 26 in FIG. 1 b, is likened to theair bubble in the example described above in FIGS. 9 a-9 f. Referringonce again to the graphical waveform depicted in FIG. 8, when the valveis in an OPENED state seal 26 is at its lowest pressure. A constant flowrate will be dispensed from the valve as illustrated by segment “1” ofthe waveform (FIG. 8) having a substantially constant slope. If thevalve is closed, the pressurized fluid from the reservoir 62 compressesthe seal 26 downward into the bore 14. Accordingly, the pressure appliedacross the seal 26 is greater when the valve is in a CLOSED state thanwhen the valve is in an OPEN state. While the valve is closed the flowrate of fluid dispensed from the valve remains unchanged as representedby the horizontal portion of the graphical waveform (segment “2”) inFIG. 8. Thereafter, the valve is reopened (segment “4”). Since the seal26 was in a compressed state when the valve was closed as a result ofthe pressurized fluid in the reservoir, upon opening the valve the seal26 first returns to its decompressed or equilibrium state. Thisdecompression is represented by vertical segment “3” of the waveform inFIG. 8 and depicts the compliance effect. Although depicted as avertical waveform, in actuality such decompression or equilibrium occursextremely quickly over a relatively short period of time. Duringdecompression of the seal 26 some accounted for fluid isdisadvantageously dispensed from the outlet-passage 22 thereby resultingin-an overdosage and compromising the overall flow rate accuracy. Oncethe pressure has been equalized, then the fluid will be dispensed fromthe outlet passage 22 at a substantially constant flow rate, once againas represented by segment “4” of the waveform having a constant slope inFIG. 8. Segment “5” of the waveform in FIG. 8 shows the valve once againin a CLOSED state as denoted by the substantially horizontal waveformwhereby the seal 26 is compressed downward due to the pressurized fluidfrom the reservoir 62.

The compliance effect resulting from decompression of the seal 26 whentransitioning from a CLOSED state to an OPEN state willdisadvantageously dispense an overdosage of fluid relative to the fluiddosage in the fluid delivery profile programmed by the user. As a resultof this overdosage, the accuracy of the flow rate dispensed from thefiuidic delivery device will be diminished or compromised. The presentinvention compensates, corrects or adjusts for the overdosage resultingfrom the compliance effect of the seal 26 thereby improving the flowrate accuracy of the fiuidic delivery device.

In addition to the compliance effect caused by the compressible seal 26,other factors may also adversely affect the accuracy of the flow rate ofthe fiuidic delivery device and may differ among fiuidic deliverydevices. One such factor is the maximum flow rate for a given fiuidicdelivery device, which is dependent on: (a) the fiuidic regulator orfiuidic restrictor, and (b) the differential pressure across the fiuidicregulator or fiuidic restrictor. Both of these parameters may differamong fiuidic delivery devices. The fiuidic regulator or fiuidicresistor 60 (as shown in FIG. 1 b) may be selected to achieve a desiredflow rate. As for the differential pressure across the fiuidicrestrictor, this value may be determined by subtracting the ambientpressure from the reservoir pressure. Once again the reservoir pressuremay vary among fluidic delivery devices. Variation in reservoir fluidpressure will impact the maximum flow rate of fluid delivered by thefluidic delivery device. Any deviation in maximum flow rate, in turn,will compromise the accuracy of the programmed flow rate of the fluidbeing dispensed from the fluidic delivery device.

Yet another parameter that has an impact on the accuracy of the flowrate for a particular fluidic delivery device is the dependencytemperature has on the pressure of the fluid in the reservoir. As thetemperature increases, the reservoir pressure increases, therefore theflow rate will increase. Here again, any change in flow rate willdiminish the flow rate accuracy of the fluid delivered from the fluidicdelivery device at a programmed fluid delivery profile.

Any given fluidic delivery device will also have an associated valveOPENING time (time required for the piezoelectric actuator to reach thevalve OPENING voltage, reference element 302 in FIG. 3 c) and valveCLOSING time (time required for the voltage across the piezoelectricactuator to drop from the 60V predetermined threshold voltage to thevalve OPENING voltage, reference element 302 in FIG. 3 c) that may varyamong fluidic delivery devices. For instance, two fluidic deliverydevices may be programmed to have the same fluid delivery profile butdifferent valve OPENING voltages (represented by reference element 302in FIG. 3 c) and associated valve OPENING times. For instance, a firstfluidic delivery device may have a valve OPENING voltage of 57V while asecond fluidic delivery device has a valve OPENING voltage of 55V. Alonger valve OPENING time (i.e., time for charge across thepiezoelectric actuator to reach the valve OPENING voltage) will berequired for the first fluidic delivery device to reach the associatedfirst valve OPENING voltage of 57V in comparison to the valve OPENINGtime for the second fluidic delivery device needed to attain theassociated second valve OPENING voltage of 55V. The longer the valveOPENING time required to reach the associated valve OPENING voltage, thelonger the time needed for the valve to remain in a valve OPENED state.Accordingly, transistor 620 in FIG. 4 will have to be driven (e.g.,switched ON/OFF) by the PWM charge input signal for a longer duration oftime. In summary, the valve OPENED time varies as a direct function ofthe valve OPENING time. That is, as the vale OPENING time increases, theduration of time for which the valve needs to remain in an OPENED stateto reach the predetermined threshold voltage of 60V also increases.Therefore, if the time for which the valve needs to remain in an OPENEDstate is not adjusted or compensated for accordingly depending on thevalve OPENING voltage and associated valve OPENING time for theparticular fiuidic delivery system, then undesirably an underdosage offluid will be dispensed or delivered thereby comprising the accuracy ofthe flow rate.

The present invention optimizes the flow rate accuracy of the fiuidicdelivery device by compensating for any one or more of these fluidicparameters. During manufacture of the valve assembly, one or morefluidic parameters (e.g., compliance effect, maximum flow rate,temperature-pressure relationship of reservoir fluid, valve OPENINGtime, and valve CLOSING time) that could have an impact on the accuracyof the flow rate is quantified or calibrated preferably for eachparticular valve assembly. Alternatively, instead of calibrating one ormore fluidic parameters for each valve assembly a constant or fixedcalibrated value may otherwise be used for all valve assembliesresulting in a less accurate flow rate. As still another alternative tospecifically calibrating the fluidic parameter, an approximation may beutilized by relying on other known parameters that need not becalibrated. Hereinafter these fluidic parameters calibrated at the timeof manufacture are collectively referred to as the “calibrated fluidicparameters” and stored in a memory associated with the fluidic deliverydevice, preferably a non-volatile memory such as a FLASH memory,described in detail below.

Specifically, the compliance effect for a particular valve assembly maybe quantified or calibrated by measuring the change in weight ofdelivered fluid from the valve assembly (Ay of segment “3” in FIG. 8) asa result of the compliance effect when transitioning the valve from aCLOSED state to an OPENED state. Alternatively, instead of measuring theweight of the dispensed fluid, the volume may be monitored based on thetime needed to fill a predefined volume when operating at a constantflow rate. In either case, the weight or volume of the fluid dispensedas a result of the compliance effect due to the seal 26 can bequantified through testing and stored in memory. The maximum flow ratemay be calibrated by merely operating the valve and monitoring how longit takes to fill a predefined volume. A temperature-pressurerelationship of the reservoir fluid may be established by monitoring thepressure of the fluid in the reservoir while varying the temperature.Lastly, the valve OPENING time of the valve assembly is dependent on thevalve OPENING voltage and may be calibrated by monitoring the period oftime it takes the piezoelectric actuator to reach the valve OPENINGvoltage. The present invention is not limited to these described methodsfor ascertaining the calibrated fluidic parameters and other methods arecontemplated. As previously mentioned, once calibrated, these fluidicparameters are stored in memory, preferably a non-volatile memory,associated with the fluidic delivery device.

Using a control device a user (e.g., patient, clinician, technician,nurse, physician) programs the fluidic delivery device to dispense afluid over time based on a programmed fluid delivery profile. The fluiddelivery profile is preferably for a 24 hour period subdivided into oneor more time intervals, each time interval being a multiple of one hourincrements of desired duration. Each time interval is preferably lessthan or equal to a maximum time interval (preferably 24 hours) butgreater than or equal to a minimum time interval (preferably one hour).For instance, the 24 hour fluid delivery profile may be subdivided into24 time intervals, each time interval 1 hour in duration. Alternatively,the 24 hour fluid delivery profile may be subdivided into 4 timeintervals, each time interval 6 hours in duration. Still yet anotherexemplary 24 hour fluid delivery profile may comprise only 2 timeintervals, the first time interval being 1 hour in duration, while thelast time interval is 23 hours. As is evident from these examples, the24 hour fluid delivery profile may be subdivided so that the timeintervals are of equal or unequal duration. Furthermore, the minimumtime interval and maximum time interval may also be programmed, asdesired. In addition to the time intervals, the user also programs theconcentration and delivery rate of the fluid to be delivered by thefluidic delivery device.

Once a fluid delivery profile has been programmed or configured by acontrol device communication is established, preferably via a wirelesscommunication interface, with the fluidic delivery device. Initially,the control unit reads any one or more of the calibrated fluidicparameters stored in a non-volatile memory device associated with thefluidic delivery device. The control device calculates, for each timeinterval of the 24 hour fluid delivery profile, two values. A firstvalue referred to as an Integer Compensated Valve OPENING Time Per Block(e.g., 400 second block) over a particular time interval. The secondvalue computed is hereinafter referred to as a Remainder CompensatedValve OPENING Time Per Hour. For a particular time interval, these twovalues are calculated by the control device based on the flow rateprogrammed by the user over that particular time interval and one ormore calibrated fluidic parameters.

An illustrative example will be described wherein the 24 hour programmedfluid delivery profile is divided into 8 time intervals, each timeinterval being 3 hours in duration. The block is set to 400 seconds induration, during which a portion of time the valve remains in an OPENEDstate and for the remaining portion of time is in a CLOSED state.

FIG. 10 is an exemplary flow diagram of the steps performed by thefluidic delivery system (FIG. 11) in adjusting the valve OPENING time(i.e., time needed for the piezoelectric actuator to reach a valveOPENING voltage, reference element 302 in FIG. 3 c) to compensate forany overdosage or underdosage of fluid delivery due to the impact one ormore of the calibrated fluidic parameters. In step 1000, processor 1110associated with the control device 1105 will determine two values: (i)an Integer Compensated Valve OPENING Time Per Block and (ii) a RemainderCompensated Valve OPENING Time Per Hour.

The Compensated Valve OPENING Time Per Hour is calculated by performingan Integer operation on the summation of Compensation Componentsassociated with any one or more of the fluidic parameters. TheCompensated Valve OPENING Time Per Hour compensating for all fivefluidic parameters is represented by the Equation (1) below:

Integer Compensated Valve OPENING Time Per Block=Integer (Maximum FlowRate Compensation Component+Valve OPENING Time CompensationComponent+Valve CLOSING Time Compensation Component+Compliance EffectCompensation Component+Temperature-Pressure Relationship CompensationComponent))  Equation (1)

The Compensation Component for each fluidic parameter will be addressedseparately.

The Maximum Flow Rate Compensation Component=(programmed flowrate/calibrated maximum flow rate)*Duration of Block

wherein,

-   programmed flow rate—is programmed by the user (e.g., physician,    technician nurse, patient). This value may be entered by the user    directly as a predetermined volume/day (e.g., mL/day) or indirectly    as a weight to be delivered/day (e.g., mg/day), whereby the    programmed flow rate may be determined by dividing the weight to be    delivered per day by the specified drug concentration level    programmed by the user.-   calibrated maximum flow rate—calibrated at the time of manufacture    of the fluidic delivery device and stored in the nonvolatile memory    associated with the fluidic delivery device. The maximum flow rate    represents the flow rate delivered by the valve when continuously    open (e.g., see FIG. 2 a). Typically, the maximum flow rate is in    the range of approximately 3.7 mL/day-4.3 mL/day).-   Duration of Block—is the duration of time in which the valve is    opened once and closed once (e.g., 400 seconds).

The next three Compensations Components (e.g., Valve OPENING TimeCompensation Component, Valve CLOSING Time Compensation Component andCompliance Effect Compensation Component) in Equation (1) will now beaddressed together. Each of these three Compensation Components may bespecifically calibrated for each fluidic delivery device. Withnegligible compromise to the accuracy of the flow rate, rather thanspecifically calibrating each of these three Compensation Components foreach fluidic delivery device, a constant value may be established foreach of these three Compensation Components and utilized for all fluidicdelivery devices. Yet a third approach may be employed as an alternativeto specifically calibrating the three Compensation Components for eachfluidic delivery device, whereby a known value is used as theCompensation Component. For instance, the rise time for the chargeapplied across the piezoelectric actuator to reach the predeterminedthreshold voltage of 60V is a known value with negligible differencecompared with the calibrated valve OPENING time and thus may be utilizedas the calibrated valve OPENING time to eliminate having to perform thisadditional calculation. Each of these three Compensation Components arealso stored in a non-volatile memory associated with the fluidicdelivery device at the time of manufacture. It is noted that thecompliance effect will result in an overdosage of fluid delivered by thefluidic delivery device and thus the Compliance Effect CompensationComponent is a negative value to reduce the valve OPENING time, whilethe valve OPENING time and valve CLOSING time will result in anunderdosage so the respective Compensation Component for each is apositive value.

Referring once again to Equation (1) the last fluidic component to beaddressed is the Temperature-Pressure Relationship CompensationComponent. At the time of manufacture, the temperature-pressurerelationship of fluid in the reservoir is characterized to determine itsimpact on the flow rate and a temperature dependent function isestablished as the Temperature-Pressure Relationship CompensationComponent.

The other value calculated by the control device is the RemainderCompensated Valve OPENING Time Per Hour by performing a MODULUSmathematical operation on (summation of the Compensation Component forone or more of the fluidic parameters, each Compensation Component beingmultiplied by the Number of Blocks in One Hour), Number of Blocks in OneHour). The Remainder Compensated Valve OPENING Time Per Hourcompensating for all five fluidic parameters is represented by theEquation (2) below:

Remainder Compensated Valve OPENING Time Per Hour=MOD (t((Maximum FlowRate Compensation Component)*Duration of the Block*Number of Blocks inOne Hour)+(Valve OPENING Time Compensation Component*Number of Blocks inOne Hour )+(Valve CLOSIGN Time Compensation Component*Number of Blocksin One Hour )+(Temperature-Pressure Relationship CompensationComponent*Number of Blocks in One Hour)), Number of Blocks in OneHour)  Equation (2)

The same variables in Equation (2) were also found in the Equation (1)and described above when calculating the Integer Compensated ValveOPENING Time Per Block and thus need not be described further.

In step 1010 of FIG. 10, the Integer Compensated Valve OPENING Time PerBlock and the Remainder Compensated Valve OPENING Time Per Hourcalculated by the control device are transmitted to the fluidic deliverydevice via a communication interface. The fluidic delivery devicereceives the Integer Compensated Valve OPENING Time Per Block andapplies it to every block in that time interval. However, in step 1020the Remainder Compensated Valve OPENING Time Per Hour is distributed bythe fluidic delivery device to those blocks within one hour such that itis as uniform as possible wherein the time distributed to any particularblock is a whole number (non-negative integer) of one or more seconds.On the one hand, if the Remainder Compensated Valve OPENING Time PerHour is a whole number that is equally divisible among the total numberof blocks in one hour without a remainder then the Remainder CompensatedValve OPENING Time Per Hour is divided by the number of blocks per hourand distributed equally to each block. On the other hand, if theRemainder Compensated Valve OPENING Time Per Hour is a whole number thatis not equally divisible among the total number of blocks in one hourwithout a remainder, it is distributed as uniformly as possible as awhole number of one or more seconds among less than all the blockswithin the one hour. For each block within one hour over the given timeinterval, in step 1030, the Total Compensated Valve OPENING time iscomputed by adding the Integer Compensated Valve OPENING Time Per Blockplus, if distributed to that particular block, the Remainder CompensatedValve OPENING time per hour.

By way of example, the valve OPENING time will be compensated for onlythree of the four fluidic parameters, namely, compliance effect, maximumflow rate and valve OPENING time/valve CLOSING time. Thetemperature-pressure dependency of the fluid in the reservoir is notcompensated for in this example.

One hour of time is divided into 9 blocks, each block 400 seconds induration.

Control device 1105 retrieves from the non-volatile memory (e.g. FLASHmemory) associated with the fluidic delivery device three calibratedparameters: compliance effect, maximum flow rate and valve OPENING time.These values are processed by the control unit to generate an IntegerCompensated Valve OPENING Time Per 400 Second Block calculated using thefollowing equation:

Integer Compensated Valve OPENING Time Per 400 Second Block=Integer((Maximum Flow Rate Compensation Value)*400+Valve Net CompensationComponent)

and, a Remainder Compensated Valve OPENING Time Per Hour calculatedusing the following equation:

Remainder Compensated Valve OPENING Time Per Hour=MOD ((((Maximum FlowRate Compensation Component)*400*9)+(Valve Net CompensationComponent*9)), 9)

As discussed above with respect to Equations (1) & (2), the Maximum FlowRate Compensation Component=(programmed flow rate/calibrated maximumflow rate)*Duration of Block.

The Valve Net Compensation Component in this example represents thesummation of the Valve OPENING Time Compensation Component, the ValveCLOSING Time Compensation Component and the Compliance EffectCompensation Component. In this example each of these, threeCompensation Components is represented as a constant value, rather thanbeing specifically calibrated for each fluidic delivery device, and thushave been combined into a single constant value referred to as Valve NetCompensation Component.

Assuming the programmed flow rate is 0.5 mL/day, the calibrated maximumflow rate is 3.95 mL/day and the calibrated Valve Net Compensation is 5seconds, then the calculated Integer Compensated Valve OPENING Time Per400 Second Block=Integer ((0.5/3.95)*400 +5)=55 seconds. The RemainderCompensated Valve OPENING Time Per Hour=MOD (((0.5/3.95)*400*9)+(5*9)),9)=5 seconds. Since the Remainder Compensated Valve OPENING Time PerHour of 5 seconds is not evenly divisible by 9 (the number of 400 secondblocks in one hour), then the 5 seconds will be distributed in onesecond intervals over the 9 blocks as uniformly as possible.Specifically, the 5 seconds will be uniformly distributed across 5 outof the 9 blocks over one hour so each of the 5 blocks has an additionalone second. The Total Compensated Valve OPENING Time Per Hour is mendetermined for each of the 9 blocks over one hour based on the IntegerCompensated Valve OPENING Time Per Block (applied to each block) and theRemainder Compensated Valve OPENING Time Per Hour (if distributed tothat particular block). A Total Compensated Valve OPENING Time for 4 ofthe 9 blocks will be set to 55 seconds while 5 of the 9 blocks will beset to 56 seconds (55 seconds+1 second).

In another example, the Integer Compensated Valve OPENING time Per Blockis calculated as 111 seconds and the Remainder Compensated Valve,OPENING Time Per Hour is 9 seconds. Since the Remainder CompensatedValve OPENING Time Per Hour (e.g., 9 seconds) is evenly divisiblewithout a remainder by the number of blocks per hour (9 blocks), each ofthe 9 blocks in one hour will have a Remainder Compensated Valve OPENINGTime Per Hour of 1 second. Thus, each of the 9 blocks, over one hourwill have a Total Compensated Valve OPENING time of 112 seconds (111seconds+1 second).

The invention described thus far is directed to improving the accuracyof the programmed flow rate for a fluidic delivery device. In keepingwith this goal it is important to monitor any inconsistencies inprogramming of the fluidic delivery device. To mitigate the risk ofincorrectly programming the fluidic delivery device, the control unitpreferably verifies the consistency of the data transmitted to thefluidic delivery device before programming the fluidic delivery device.As discussed in detail above, the Integer Compensated Valve OPENING TimePer Block (Equation (1)) and Remainder Compensated Valve OPENING TimePer Hour (Equation (2)) are both calculated by the control device basedon the fluidic calibration parameters stored in a non-volatile memoryassociated with the fluidic delivery device. The source code programmingsteps for each of these two equations is provided twice or duplicated inthe programming code for processor 1110 (FIG. 11). The first iterationor calculation of Equations (1) and (2) is performed using a firstportion of the programming source code. Before programming the fluidicdelivery device, the control device verifies that these same two valuesare obtained by recalculating Equations (1) and (2) using source codeprogramming steps set forth in a second portion of the programmingsource code, different from the first portion. This redundant processingmitigates the risk of a programming failure by verifying the flow dataintegrity prior to transmission.

In order to further reduce the risk of incorrectly programming the fluiddelivery device, additional checks may be performed using a specificmemory architecture as shown in FIG. 11 for the fluidic delivery system1100. System 1100 includes an implantable drug infusion delivery device1120 programmed by an external control device 1105 via a wirelesscommunication interface. Implantable drug infusion delivery device 1120includes three controllers or processors 1125, 1130, 1135, however, anynumber of one or more controllers or processors may be used, as desired.Each controller has associated therewith a volatile memory device suchas a RAM and a non-volatile memory device, for example, a FLASH memory.A first, primary of main controller 112 has a volatile RAM memory 145and a non-volatile FLASH memory 1150. Any number of one or moresecondary or auxiliary controllers may be included. In the example,there are two secondary or auxiliary controllers, e.g., a secondcontroller 1130 and a third controller 1135. Similar to the primary,first or main controller 1125, each secondary or auxiliary controller1130, 1135 also has a volatile RAM and a non-volatile FLASH memory. Alsoassociated with the implantable drug infusion delivery device 1120 butexternal to the controllers 1125, 1130, 1135 is a non-volatile EEPROM1140 electrically connected to the main controller 1125.

The calibrated fluidic parameters (e.g., compliance effect, maximum flowrate, temperature-pressure relationship of reservoir fluid and openingvoltage rise time) are stored in the non-volatile FLASH memory 1150associated with the main controller 1125. The values calculated by thecontrol device (e.g., the Integer Compensated Valve OPENING Time PerBlock and the Remainder Compensated Valve OPENING Time Per Hour) arereceived by the implantable drug infusion delivery device 1120 andstored in the non-volatile EEPROM memory 1140 associated therewith.

During self-testing, preferably once a day, the implantable druginfusion delivery device 1120 calculates a FLASH code memory CRC andcompares this calculated value with the FLASH code memory CRC that waspreviously stored in the FLASH memory 1150 when the implantable druginfusion delivery device 1120 was programmed during manufacturing. Ifthe calculated CRC doesn't match with the previously stored CRC valuefor the FLASH code memory, then a FLASH code error is set, an alarm isengaged and delivery of the drug ceases. This process allows checkingfor corruption of the fluid calibration parameters stored in thenon-volatile FLASH memory 1150.

In order to minimize power consumption, the main controller 1125 ispowered off until awakened when required to perform processing. Wheneverthe main controller wakes up it copies the entire contents of thenon-volatile EEPROM memory 1140 to volatile RAM memory 1145. Whenreading the contents of the EEPROM memory 1140, the main controller 1125calculates the EEPROM checksum and verifies it with the previouslystored checksum in the EEPROM memory. If the calculated checksum doesn'tmatch with the previously stored checksum in the EEPROM, then the EEPROMerror code is set, an alarm is engaged and drug delivery ceases. Suchverification processing will detect corruption of the fluid deliveryprofile since the Integer Compensated Valve OPENING Time Per Block andthe Remainder Compensated Valve OPENING Time Per Hour for every timeinterval comprising the fluid delivery profile is stored in EEPROMmemory 1140.

Upon a reset event triggered by any of the controllers, the othersecondary controllers (other than the main controller 1125) also copythe drug delivery profile data from the EEPROM 1140 into theirrespective associated RAM, either via a direct path (e.g., EEPROMdirectly to RAM associated with secondary controller) or through anindirect path (e.g., EEPROM to RAM associated with main controller toRAM associated with secondary controller).

As explained above, the EEPROM 1140 and the secondary controllers (otherthan the main controller 1125) commonly store the same drug deliveryprofile data in their respective RAM memories. The drug delivery profiledata is stored in the EEPROM 1140 of the main controller 1125 because itreceives the information from the control device 1105. For instance, themain controller 1125 programs the second controller 1130 with the samedrug delivery profile, because the second controller 1130 drives thevalve. The same drug delivery profile is stored in the third controller1135 as well. During daily self-testing of the implantable drug infusiondelivery device 1120, the drug delivery profile data is stored in theEEPROM 1140 as well as in the volatile RAM associated with each of thecontrollers. If during self-testing there is a discrepancy between thedrug profile data stored in EEPROM 1140 and that stored in any of thevolatile RAMs of any of the controllers, an alarm will be activated anddrug delivery will cease.

Any of the previously described methods may be employed separately orused in any combination thereof for mitigating the risk of delivery ofthe fluid from the fluidic delivery device at an incorrect flow rate. Inthe first instance, the fluid delivery profile data is verified prior toprogramming the fluidic delivery device, whereas the second additionalmethod checks the consistency of the fluid delivery device profilestored in the memory associated with the fluidic delivery device,preferably at least once a day.

Thus, while there have been shown, described, and pointed outfundamental novel features of the invention as applied to a preferredembodiment thereof, it will be understood that various omissions,substitutions, and changes in the form and details of the devicesillustrated, and in their operation, may be made by those skilled in theart without departing from the spirit and scope of the invention. Forexample, it is expressly intended that all combinations of thoseelements and/or steps that perform substantially the same function, insubstantially the same way, to achieve the same results be within thescope of the invention. Substitutions of elements from one describedembodiment to another are also fully intended and contemplated. It isalso to be understood that the drawings are not necessarily drawn toscale, but that they are merely conceptual in nature. It is theintention, therefore, to be limited only as indicated by the scope ofthe claims appended hereto.

Every issued patent, pending patent application, publication, journalarticle, book or any other reference cited herein is each incorporatedby reference in their entirety.

1. A method for optimizing flow rate accuracy of a fluidic deliverysystem by compensating for at least one fluidic parameter effecting theflow rate accuracy of fluid dispensed by a valve, a block representing apredetermined duration of time over which the valve opens once andcloses once, the valve being associated with a fluidic delivery deviceincluding a first fluidic delivery device processor and a firstnon-volatile memory device having stored therein at least one calibratedfluidic parameter determined for the fluidic delivery device, thefluidic delivery device being programmable by a control device having acontrol device processor, the method comprising the steps of: (a)calculating using the control device processor an Integer CompensatedValve OPENING Time Per Block and a Remainder Compensated Valve OpeningTime Per Predetermined Time Interval based on the at least onecalibrated fluidic parameter retrieved from the first non-volatilememory device; (b) transmitting from the control device to the fluidicdelivery device the calculated Integer Compensated Valve OPENING TimePer Block and the Remainder Compensated Valve Opening Time PerPredetermined Time Interval; (c) distributing the Remainder CompensatedValve OPENING Time Per Predetermined Time Interval as uniformly aspossible to those blocks in the predetermined time interval; (d)determining for each block per predetermined time interval a TotalCompensated Valve OPENING Time by adding the Integer Compensated ValveOPENING Time Per Block and, if distributed to that particular block inthe predetermined time interval, the uniformly as possible distributedRemainder Compensated Valve OPENING Time Per Predetermined TimeInterval; and (e) optimizing the flow rate accuracy of the fluidicdelivery device by opening the valve based on the Total CompensatedValve OPENING time which has compensated for the fluidic parameters. 2.The method in accordance with claim 1, wherein the at least onecalibrated fluidic parameter for the fluidic delivery device is storedin the first non-volatile memory device at a time of manufacture of thefluidic delivery device.
 3. The method in accordance with claim. 1,wherein-the at least one calibrated fluidic parameters comprises atleast one of compliance effect, maximum flow rate, temperature-pressurerelationship of reservoir fluid, valve OPENING time, and valve CLOSINGtime.
 4. The method in accordance with claim 1, wherein the IntegerCompensated Valve OPENING Time Per Block is determined as: IntegerCompensated Valve OPENING Time Per Block=Integer (Maximum Flow RateCompensation Component+Valve OPENING Time Compensation Component+ValveCLOSING Time Compensation Component+Compliance Effect CompensationComponent+Temperature-Pressure Relationship Compensation Component). 5.The method in accordance with claim 4, wherein the Maximum Flow RateCompensation Component is determined as: Maximum Flow Rate CompensationComponent=(programmed flow rate/calibrated maximum flow rate)*Durationof Block wherein, the programmed flow rate is programmed by the user;the calibrated maximum flow rate is calibrated at a time of manufactureof the fluidic delivery; and the Duration of Block is a duration of timefor the block in which the valve is opened once and closed once.
 6. Themethod in accordance with claim 5, wherein the Remainder CompensatedValve Opening Time Per Predetermined Time Interval is determined as:Remainder Compensated Valve OPENING Time Per Predetermined TimeInterval=MOD ((((Maximum Flow Rate Compensation Component)*Duration ofthe Block*Number of Blocks in the predetermined time interval)+(ValveOPENING Time Compensation Component*Number of Blocks in thepredetermined time interval )+(Valve CLOSING Time CompensationComponent*Number of Blocks in the predetermined timeinterval)+(Temperature-Pressure Relationship CompensationComponent*Number of Blocks in the predetermined time interval)), Numberof Blocks in the predetermined time interval).
 7. The method inaccordance with claim 1, wherein step (c) comprises the steps of: if theRemainder Compensated Valve OPENING Time Per Predetermined Time Intervalis a whole number equally divisible among the total number of blocks inthe predetermined time interval without a remainder, diving theRemainder Compensated Valve OPENING Time Per Predetermined Time Intervalby the number of blocks per predetermined time interval and distributingequally to each block; and if the Remainder Compensated Valve OPENINGTime Per Predetermined Time Interval is a whole number that is notequally divisible among the total number of blocks in the predeterminedtime interval without a remainder, distributing as uniformly as possibleas a whole number of one or more seconds among less than all the blockswithin the predetermined time interval.
 8. The method in accordance withclaim 1, wherein in step (a) the Integer Compensated Valve OPENING TimePer Block and Remainder Compensated Valve OPENING Time Per PredeterminedTime Interval are calculated by the control device processor twice toverify the consistency of the data prior to being transmitted to thefluidic delivery device.
 9. The method in accordance with claim 8,wherein verification of the consistency of the data comprises the stepsof performing a first calculation of the Integer Compensated ValveOPENING Time Per Block and Remainder Compensated Valve OPENING Time PerPredetermined Time Interval using a first portion of the programmingsource code for the control device processor, and performing a secondcalculation of the Integer Compensated Valve OPENING Time Per Block andRemainder Compensated Valve OPENING Time Per Predetermined Time Intervalusing a second portion of the programming source code of the controldevice processor, different than the first portion.
 10. The method inaccordance with claim 1, wherein the Integer Compensated Valve OPENINGTime Per Block and Remainder Compensated Valve OPENING Time PerPredetermined Time Interval are stored in a second non-volatile memorydevice associated with the fluidic delivery device.
 11. The method inaccordance with claim 10, wherein the first non-volatile memory deviceis a FLASH memory and the second non-volatile memory device is anEEPROM.
 12. The method in accordance with claim 11, further comprisingthe step of checking for corruption of the at least one calibratedfluidic parameters stored in the FLASH memory by calculating a FLASHcode memory CRC and comparing this calculated value with a FLASH codememory CRC previously stored in the FLASH memory at the time ofmanufacture of the fluidic delivery device.
 13. The method in accordancewith claim 12, wherein the checking of the FLASH memory occurs duringself-testing of the fluidic delivery device.
 14. The method inaccordance with claim 11, wherein the first fluidic delivery deviceprocessor has an associated RAM, the method further comprising the stepsof: copying entire contents of the EEPROM to the RAM; and calculatingthe EEPROM checksum and verifying the calculated value with a previouslystored checksum in the EEPROM.
 15. The method in accordance with claim11, wherein the fluidic delivery device has at least one additionalprocessor, each of the at least one additional processors having anassociated FLASH memory and an associated RAM, the method furthercomprising the steps of: storing drug delivery profile data receivedfrom the control device in the EEPROM; during reset of any of theprocessors, copying drug delivery profile data stored in the EEPROM tothe respective associated RAMs of each of the processors; and duringself-testing of the fluidic delivery device detecting any discrepancybetween the drug profile data stored in EEPROM and that stored in any ofthe RAMs in the associated processors.
 16. A fluidic delivery systemwith optimized flow rate accuracy by compensating for at least onefluidic parameter effecting the flow rate accuracy of fluid dispensed bya valve, a block representing a predetermined duration of time overwhich the valve opens once and closes once, comprising: a control devicehaving a control device processor; and a fluidic delivery deviceincluding the valve, a first fluidic delivery device processor and afirst non-volatile memory device for storing the flow rate and at leastone calibrated fluidic parameter associated with the fluidic deliverydevice; the fluidic delivery device being programmed by the controldevice; the control device processor being programmed to: (a) calculateusing the control device processor an Integer Compensated Valve OPENINGTime Per Block and a I Remainder Compensated Valve Opening Time PerPredetermined Time Interval based on the at least one calibrated fluidicparameter retrieved from the first non-volatile memory device; (b)transmit from the control device to the fluidic delivery device thecalculated Integer Compensated Valve OPENING Time Per Block and theRemainder Compensated Valve Opening Time Per Predetermined TimeInterval; the first fluidic delivery device processor being programmedto: (c) distribute the Remainder Compensated Valve OPENING Time PerPredetermined Time Interval as uniformly as possible to those blocks inthe predetermined time interval; (d) determine for each block per thepredetermined time interval a Total Compensated Valve OPENING Time byadding the Integer Compensated Valve OPENING Time Per Block and, ifdistributed to that particular block in the predetermined time interval,the uniformly as possible distributed Remainder Compensated ValveOPENING Time Per Predetermined Time Interval; and (e) optimize the flowrate accuracy of the fluidic delivery device by opening the valve basedon the Total Compensated Valve OPENING time which has compensated forthe fluidic parameters.
 17. The system in accordance with claim 16,wherein the at least one calibrated fluidic parameter for the fluidicdelivery device is stored in the first non-volatile memory device at atime of manufacture of the fluidic delivery device.
 18. The system inaccordance with claim 16, wherein the at least one calibrated fluidicparameters comprises at least one of compliance effect, maximum flowrate, temperature-pressure relationship of reservoir fluid, valveOPENING time, and valve CLOSING time.
 19. The system in accordance withclaim 16, wherein the programming of the first fluidic delivery deviceprocessor to calculate the Integer Compensated Valve OPENING Time PerBlock is determined as: Integer Compensated Valve OPENING Time PerBlock=Integer (Maximum Flow Rate Compensation Component+Valve OPENINGTime Compensation Component+Valve CLOSING Time CompensationComponent+Compliance Effect Compensation Component+Temperature-PressureRelationship Compensation Component).
 20. The system in accordance withclaim 19, wherein the programming of the first fluidic delivery deviceprocessor to calculate the Maximum Flow Rate Compensation Component isdetermined as: Maximum Flow Rate Compensation Component=(programmed flowrate/calibrated maximum flow rate)*Duration of Block wherein, theprogrammed flow rate is programmed by the user; the calibrated maximumflow rate is calibrated at a time of manufacture of the fluidicdelivery; and the Duration of Block is a duration of time for the blockin which the valve is opened once and closed once.
 21. The system inaccordance with claim 20, wherein the programming of the first fluidicdelivery device processor to calculate the Remainder Compensated ValveOpening Time Per Predetermined Time Interval is determined as: RemainderCompensated Valve OPENING Time Per Predetermined Time Interval=MOD((((Maximum Flow Rate Compensation Component)*Duration of theBlock*Number of Blocks in the predetermined time interval)+(ValveOPENING Time Compensation Component*Number of Blocks in thepredetermined time interval)+(Valve CLOSING Time CompensationComponent*Number of Blocks in the predetermined timeinterval)+(Temperature-Pressure Relationship CompensationComponent*Number of Blocks in the predetermined time interval)), Numberof Blocks in the predetermined time interval)
 22. The system inaccordance with claim 16, wherein the programming of the fluidicdelivery device processor to distribute the Remainder Compensated ValveOPENING Time Per Predetermined Time Interval comprises the functions of:if the Remainder Compensated Valve OPENING Time Per Predetermined TimeInterval is a whole number equally divisible among the total number ofblocks in the predetermined time interval without a remainder, dividingthe Remainder Compensated Valve OPENING Time Per Predetermined TimeInterval by the number of blocks per the predetermined time interval anddistributing equally to each block; and if the Remainder CompensatedValve OPENING Time Per Predetermined Time Interval is a whole numberthat is not equally divisible among the total number of blocks in thepredetermined time interval without a remainder, distributing asuniformly as possible as a whole number of one or more seconds amongless than all the blocks within the predetermined time interval.
 23. Thesystem in accordance with claim 16, wherein me programming of thecontrol device processor to calculate the Integer Compensated ValveOPENING Time Per Block and Remainder Compensated Valve OPENING Time PerPredetermined Time Interval are calculated by the control deviceprocessor twice to verify the consistency of the data prior to beingtransmitted to the fluidic delivery device.
 24. The system in accordancewith claim 23, wherein the consistency of the calculated IntegerCompensated Valve OPENING Time Per Block and Remainder Compensated ValveOPENING Time Per Predetermined Time Interval is verified by performing afirst calculation of the Integer Compensated Valve OPENING Time PerBlock and Remainder Compensated Valve OPENING Time Per PredeterminedTime Interval using a first portion of the programming source code forthe control device processor, and performing a second calculation of theInteger Compensated Valve OPENING Time Per Block and RemainderCompensated Valve OPENING Time Per Predetermined Time Interval using asecond portion of the programming source code of the control deviceprocessor, different than the first portion.
 25. The system inaccordance with claim 16, wherein the Integer Compensated Valve OPENINGTime Per Block and Remainder Compensated Valve OPENING Time PerPredetermined Time Interval are stored in a second non-volatile memoryassociated with the fluidic delivery device.
 26. The system inaccordance with claim 25, wherein the first non-volatile memory deviceis a FLASH memory and the second non-volatile memory device is anEEPROM.
 27. The system in accordance with claim 26, wherein the firstfluidic delivery device processor is programmed to check for corruptionof the at least one calibrated fluidic parameters stored in the FLASHmemory by calculating a FLASH code memory CRC and comparing thiscalculated value with a FLASH code memory CRC previously stored in theFLASH memory at the time of manufacture of the fluidic delivery device.28. The system in accordance with claim 27, wherein the checking of theFLASH memory occurs during self-testing of the fluidic delivery device.29. The system in accordance with claim 26, wherein the first fluidicdelivery processor has an associated RAM, the first fluidic deliverydevice processor is programmed to: copy entire contents of the EEPROM tothe RAM; calculate the EEPROM checksum; and verify the calculated EEPROMchecksum with a previously stored checksum in the EEPROM.
 30. The systemin accordance with claim 26, wherein the fluidic delivery device has atleast one additional processor, each of the at least one additionalprocessors having an associated FLASH memory and an associated RAM;wherein the EEPROM stores drug delivery profile data received from thecontrol device; and wherein the first fluidic delivery processor isprogrammed to: copy drug delivery profile data stored in the EEPROM tothe respective associated RAMs of each of the processors, during resetof any of the processors; and detect any discrepancy between the drugprofile data stored in EEPROM and that stored in any of the RAMs in theassociated processors, during self-testing of the fluidic deliverydevice.
 31. A valve assembly, comprising: a power supply; charge pumpcircuitry powered by the power supply; a piezoelectric actuator chargedby the charge pump circuitry, the charge applied across thepiezoelectric actuator reaching a predetermined opening voltagethreshold over a predetermined opening voltage rise time; and a valvetransitioning from a CLOSED state to an OPENED state when thepiezoelectric actuator exceeds the predetermined opening voltagethreshold, a block representing a predetermined duration of time overwhich the valve opens once and closes once; the piezoelectric actuatorconsuming energy from the power supply only during the predeterminedopening voltage rise time while the piezoelectric actuator is chargingprior to reaching the predetermined threshold voltage, wherein thepredetermined rise time is less than the block.
 32. The valve assemblyiii accordance with claim 31, wherein the predetermined thresholdvoltage is approximately 60 V.
 33. The valve assembly in accordance withclaim 31, further comprising at least one relatively low leakage diodeelectrically connected to the piezoelectric actuator to retain thecharge applied to the piezoelectric actuator with minimal leakage. 34.The method in accordance with claim 1, wherein the predetermined timeinterval is one hour.
 35. The system in accordance with claim 16,wherein the predetermined time interval is one hour.